1. Field of the Invention
The field of art to which this invention pertains is the solid bed adsorptive separation of monosaccharides. More specifically, the invention relates to a process for separating arabinose from a mixture comprising arabinose and one or more additional aldoses, which process employs an adsorbent comprising a nuclearly sulfonated cation exchange resin having a crosslinked vinylaromatic resin matrix to selectively adsorb arabinose from the feed mixture.
2. Description of the Prior Art
This invention is particularly concerned with the separation of arabinose from other monosaccharides. Obtaining pure L-arabinose has commercial significance in light of its potential as a starting material for the production of L-glucose, a possible non-nutritive sweetener. Furthermore, L-arabinose is one of the few L-sugars available freely in nature, such as from sugar beet pulp and rice hulls, and therefore useful in synthesizing possibly non-nutritive sweeteners, such as L-glucose. Another common source of arabinose is the hydrolysis of hemicellulose in making pulp from wood which yields a mixture of L-arabinose, mannose and xylose. L-Arabinose, mixed with D-galactose and sucrose, are the products of a biomass operation to convert sugar beets to sugars. Regardless of the source, the arabinose is typically found in a mixture of many monosaccharides. Therefore, it is highly desirable to have a simple method for separating arabinose from the other monosaccharides present in the source mixture. However, in light of the ultimate food use of products made from arabinose, the separation process must not introduce contaminants that will render the arabinose or subsequent products unsuitable for human consumption.
Specific methods for separating arabinose are known in the art. U.S. Pat. No. 3,160,624 discloses the separation of D(L)-arabinose from D(L)-ribose by chromatography using a cellulose powder or ion exchanged resin. However, it is well known in the art that heretofore resin or cellulose adsorbents posed significant operational problems when their use is attempted on a large scale due to the high pressure drops associated with their use. However, newly developed methods of forming the ion exchange resins into very uniform spheres, as in U.S. Pat. No. 4,444,961 referred to hereinafter, reduce this tendency to cause high pressure drops. The zeolite adsorbents which are commonly used in large scale adsorptive separation processes have also been applied to the separation of arabinose from other mixtures of monosaccharides. U.S. Pat. No. 4,516,566 is directed to the separation of L-arabinose from a mixture of sugar that exists in the hydrolysates of wood and beet pulp using an X type zeolite exchanged with barium cations as an adsorbent. It is also disclosed in U.S. Pat. No. 4,471,114, at column 7, lines 31-44 that arabinose can be separated from mannose plus other sugars in two stages with a barium-exchanged X zeolite. A calcium-exchanged ion exchange resin (Dowex 50-W-X8) has been reported to separate arabinose from xylose and the carbonate form reported to separate arabinose from xylose, ribose and lyxose. P. Jandera et al., J. of Chromatography, 98 (1974) 55-104, p. 81.
In contradistinction to these findings, it has been discovered that nuclearly sulfonated cation exchange resins having a crosslinked vinylaromatic resin matrix will selectively adsorb arabinose from other monosaccharide aldoses. Moreover, the use of these ion exchange resins exchanged with a Ca--NH.sub.4 mixture of cations allows the purification and recovery of arabinose that is acceptable to the food industry.